forked from mirrors/docker-distribution
c4d69174ee
The UUID generation retries multiple times to read a full UUID, but preserves any bytes of entropy he successfully managed to read between retries. Signed-off-by: Arnaud Porterie <arnaud.porterie@docker.com>
127 lines
3 KiB
Go
127 lines
3 KiB
Go
// Package uuid provides simple UUID generation. Only version 4 style UUIDs
|
|
// can be generated.
|
|
//
|
|
// Please see http://tools.ietf.org/html/rfc4122 for details on UUIDs.
|
|
package uuid
|
|
|
|
import (
|
|
"crypto/rand"
|
|
"fmt"
|
|
"io"
|
|
"log"
|
|
"os"
|
|
"syscall"
|
|
"time"
|
|
)
|
|
|
|
const (
|
|
// Bits is the number of bits in a UUID
|
|
Bits = 128
|
|
|
|
// Size is the number of bytes in a UUID
|
|
Size = Bits / 8
|
|
|
|
format = "%08x-%04x-%04x-%04x-%012x"
|
|
)
|
|
|
|
var (
|
|
// ErrUUIDInvalid indicates a parsed string is not a valid uuid.
|
|
ErrUUIDInvalid = fmt.Errorf("invalid uuid")
|
|
|
|
// Loggerf can be used to override the default logging destination. Such
|
|
// log messages in this library should be logged at warning or higher.
|
|
Loggerf = log.Printf
|
|
)
|
|
|
|
// UUID represents a UUID value. UUIDs can be compared and set to other values
|
|
// and accessed by byte.
|
|
type UUID [Size]byte
|
|
|
|
// Generate creates a new, version 4 uuid.
|
|
func Generate() (u UUID) {
|
|
const (
|
|
// ensures we backoff for less than 450ms total. Use the following to
|
|
// select new value, in units of 10ms:
|
|
// n*(n+1)/2 = d -> n^2 + n - 2d -> n = (sqrt(8d + 1) - 1)/2
|
|
maxretries = 9
|
|
backoff = time.Millisecond * 10
|
|
)
|
|
|
|
var (
|
|
totalBackoff time.Duration
|
|
count int
|
|
retries int
|
|
)
|
|
|
|
for {
|
|
// This should never block but the read may fail. Because of this,
|
|
// we just try to read the random number generator until we get
|
|
// something. This is a very rare condition but may happen.
|
|
b := time.Duration(retries) * backoff
|
|
time.Sleep(b)
|
|
totalBackoff += b
|
|
|
|
n, err := io.ReadFull(rand.Reader, u[count:])
|
|
if err != nil {
|
|
if retryOnError(err) && retries < maxretries {
|
|
count += n
|
|
retries++
|
|
Loggerf("error generating version 4 uuid, retrying: %v", err)
|
|
continue
|
|
}
|
|
|
|
// Any other errors represent a system problem. What did someone
|
|
// do to /dev/urandom?
|
|
panic(fmt.Errorf("error reading random number generator, retried for %v: %v", totalBackoff.String(), err))
|
|
}
|
|
|
|
break
|
|
}
|
|
|
|
u[6] = (u[6] & 0x0f) | 0x40 // set version byte
|
|
u[8] = (u[8] & 0x3f) | 0x80 // set high order byte 0b10{8,9,a,b}
|
|
|
|
return u
|
|
}
|
|
|
|
// Parse attempts to extract a uuid from the string or returns an error.
|
|
func Parse(s string) (u UUID, err error) {
|
|
if len(s) != 36 {
|
|
return UUID{}, ErrUUIDInvalid
|
|
}
|
|
|
|
// create stack addresses for each section of the uuid.
|
|
p := make([][]byte, 5)
|
|
|
|
if _, err := fmt.Sscanf(s, format, &p[0], &p[1], &p[2], &p[3], &p[4]); err != nil {
|
|
return u, err
|
|
}
|
|
|
|
copy(u[0:4], p[0])
|
|
copy(u[4:6], p[1])
|
|
copy(u[6:8], p[2])
|
|
copy(u[8:10], p[3])
|
|
copy(u[10:16], p[4])
|
|
|
|
return
|
|
}
|
|
|
|
func (u UUID) String() string {
|
|
return fmt.Sprintf(format, u[:4], u[4:6], u[6:8], u[8:10], u[10:])
|
|
}
|
|
|
|
// retryOnError tries to detect whether or not retrying would be fruitful.
|
|
func retryOnError(err error) bool {
|
|
switch err := err.(type) {
|
|
case *os.PathError:
|
|
return retryOnError(err.Err) // unpack the target error
|
|
case syscall.Errno:
|
|
if err == syscall.EPERM {
|
|
// EPERM represents an entropy pool exhaustion, a condition under
|
|
// which we backoff and retry.
|
|
return true
|
|
}
|
|
}
|
|
|
|
return false
|
|
}
|